Device for measuring oxygen concentration of molten metal

ABSTRACT

A DEVICE FOR MEASURING OXYYGEN CONCENTRATION OF MOLTEN METAL BY USING AN OXYGEN CONCENTRATION CELL, WHEREIN A SOLID ELECTROLYTE IS DIRECTLY OR INDIRECTLY COVERED WITH A MATERIAL TO BE CARBONIZED IN THE MOLTEN METAL, SO THAT THE ELEMENT MAY BE GRADUALLY HEATED BEFORE COMING IN CONTACT WITH THE MOLTEN METAL. THE ELECTRIC CONNECTION OF THE SOLID ELECTROLYTE TO AN INDICATOR MAY SIMULTANEOUSLY BE ACCOMPLISHED WITH ITS MECHANICAL CONNECTION TO A STANDARD GAS SOURCE. A SPECIMEN OF THE CLEAN MOLTEN METAL CAN BE COLLECTED FROM SUBSTANTIALLY THE SAME SPOT WHERE THE OXYGEN CONCENTRATION IS MEASURED.

3 Sheets-Sheet UW mm MAKOTO NODA ET AL` Feb, 12, 1974 DEVICE EOR MEASURING OXYGEN CONCENTRATION OE MOLTEN METAL Filed July 2l, 1971 Feb. l2, 1974 MAKOTQ NODA ETAL 3,791,954

DEVICE FOR MEASURING OXYGEN CONCENTRATION OF MOLTEN METAL 3 Sheets-Sheet 2 Filed July 2l, 1971 FIG Feb. l2, 1974 MAKoTo Nom ET Al- 3,'79L954 DEVICE FOR MEASURING OXYGEN CONCENTRATION OF MOLTEN METAL Filed July 21, 1971 3 sheets-sheet s A IILA United States Patent O DEVICE FOR MEASURING OXYGEN CONCEN- TRATION 0F MOLTEN METAL Makoto Noda, Nagoya, and Takeshi Kajita, Ohaza-Yuki, Japan, assignors to NGK Insulators, Ltd., Nagoya,

Ja an P Filed July 21, 1971, Ser; No. 164,655 vClaims priority, application Japan, Aug. 6, 1970, t/68,293, 45/68,294; Oct. 23, 1970, 45/92,842;

May 7, 197146/36,504, 46/36,505

Int. Cl. G01n 27/46 U.S. Cl. 204-195 S 7 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND 0F THE 'INVENTION Field of the invention This invention relates to a device for measuring oxygen concentration of molten metal, and more particularly to a^d`evice for measuring oxygen concentration of molten metal by using an oxygen concentration cell with a solid electrolyte.

` yIt'is well known to make van oxygen concentration cell by a solid electrolyte consisting essentially of a solid solutionof at least one oxide selected from the group consisting of zirconium oxide (ZrO2), hafnium oxide (Hf-O2), cerium oxide (Ce02), and thorium oxide (ThO2), and at least one oxide selected from the group consisting of magnesium oxide (MgO), calcium oxide (CaO), yttrium oxide (Y2O3), lanthanum oxide (La203), neodymium oxide (Nd203), barium oxide (BaO), strontium oxide (SrO), selenium oxide (Se203), ytterbium oxide (Yb2O3), and samarium oxide (Sm203). Theoretically, the` EMF of such solid electrolyte at a temperature T( K.) for an oxygen partial pressure ratio P2/P1 across its opposite surfaces is given as follows:

' RAT P2 n EMF 4F P1 Here, R is the gas constant, and F is the Faraday constant. l i

v Basedon the above equation, it is possible to determine an unknown oxygen partial pressure P2 by measuring the EMF and the temperature while exposing the solid electrolyte to a known oxygen partial pressure P1 at its one surface and to the unknown oxygen partial pressure P2 atV its opposite surface. Therefore, it is possible to determine an unknown oxygen concentration, based on the partial pressure thus determined.

` TheI concentration of free oxygen (namely, oxygen concentration) in a molten metal can be determinedby using such a solid electrolyte, based on the aforesaid principles; for instance, voltage-oxygen concentration curves may be predetermined for a given solid electrolyte so that an unknown oxygen concentration may be determined by measuring the EMF of the electrolyte while exposing it to the unknown oxygen concentration and entering the EMF to the predetermined curves.

. Patented Feb. 12, 1974 ICC Actually, measurement of the oxygen concentration in molten metal is carried out by dipping a solid electrolyte therein, which electrolyte is secured to the tip of a tubular holder made of refractory material, such as alumina porcelain or quartz glass.

Description of the prior art Conventional devices for measuring the oxygen concentration of molten metal by using a solid electrolyte have a shortcoming in that the solid electrolyte is highly susceptible to cracks due to the thermal shock when it is dipped into the molten metal. In order to avoid such cracks, it has been practiced to preheat the solid electrolyte secured to the tip of its holder before dipping it into a molten metal. Such preheating, however, is not only time-consuming but also unreliable, because its success depends on the operators skill and experience.

The conventional devices are also susceptible to measuring errors due to the presence of slag on the top surface of molten metal being measured. More particularly, when the solid electrolyte carried by a tubular holder is dipped into the molten metal, it passes through a layer of slag iloating on the surface of the molten metal, and such slag sticks to the surface of the solid electrolyte so as to prevent the molten metal from coming in direct contact with the solid electrolyte. The presence of slag between the molten metal and the solid electrolyte tends to cause an error in the measurement.

With the conventional devices for measuring oxygen concentration of molten metal by using solid electrolyte, it has been noticed that the gastight joint between the solid electrolyte and the tip of its holder is rather quickly deteriorated due to the difference of the thermal expansion therebetween when the device is dipped into the molten metal. Therefore, the oxygen gas partial pressure ratio across the solid electrolyte is affected and an error is caused in the measurement of the oxygen gas concentration.

Various approaches have been tried for improving the bondage, gastightness, and refractory adhesive of the joint between the solid electrolyte and its holder. For instance, the oxides constituting the solid electrolyte is granulated, so as to have a certain grain size distribution, and the oxide thus granulated is made into a paste by kneading it while adding a solution of a phosphate or acetate of that metal whose oxide constitutes the solid electrolyte, which paste is stuffed in the gap between the solid electrolyte and its holder. The salts in the paste are decomposed by a high temperature to obtain desired improvement of the bondage, gastightness, and the refractory adhesive of the aforesaid joint. Furthermore, it has also been tried to further improve the bondage and gastightness of the aforesaid joint by causing heat-shrinkage at the tip of the tubular holder of the solid electrolyte by using hightemperature flame of oxygen and hydrogen. Despite such efforts, it is impossible to establish accurate coincidence of the thermal expansion between the solid electrolyte and its tubular holder. Accordingly, it is still very dillicult to ensure high gastightness between the electrolyte and its tubular holder by completely eliminating the risk of generating minute gaps therebetween due to the dilerence of thenmal expansion therebetween. Y j

In conventional oxygen concentration measuring de# vices, an elongated hollow protective tube made of steel or bias-wound paper is used tfor facilitating the immersion the solid electrolyte secured to the'tip of the tubular holder into molten metal. (Such steel and paper tubes are thereof, and the molten metal flows into the'paper tuberin to 20 seconds after dipping into the molten metal. Accordingly, if any measuring means protected by such a paper tube is kept in the molten metal more than 15 to 20 seconds, the measuring means is likely to be damaged by the molten metal rushing into the protective tube.

It is preferable to correct the value deter-mined by the solid electrolyte for the effect caused by co-existing elements.

Other elements co-existing in the molten metal may affect the measurement of free oxygen therein, so that the value of the oxygen concentration determined by the solid electrolyte should preferably be corrected for such effect of other elements. To this end, a specimen for chemical analysis is taken `from the molten metal by using a clipper, so as to determine the contents of other elements co-existing in the molten metal at the time of the measurement. The conventional dipper for taking such specimens, however, has a shortcoming in that they take slag together with the molten metal, so that the chemical analysis of .the specimen taken by such dipper does not provide the true contents of various elements of the molten metal, but the result of the chemical analysis is likely to be affected by the slag. Accordingly, the accuracy of the correction by using such la conventional dipper is rather low.

The amount of total oxygen in the form of free oxygen and oxides, such as ferric oxide (FezOa), aluminum oxide (A1203) and so on, in the molten metal is also determined by means of chemical analysis or radio-activation analysis for comparison with the free oxygen concentration determined by the solid electrolyte. The specimen, however, is likely to contain slag, because when the dipper is removed from the molten metal the clipper scoops slag floating on the surface of the molten metal. Thus, the sample does not represent the true composition of the molten metal, and the accuracy or significance of the amount of total oxygen as determined by using such sample is fairly low. A special clipper may be used for taking pure specimen without any slag, for improving the accuracy of the amount of the total oxygen, but if such dipper takes specimen at a position distant from the position of the oxygen concentration cell, the merit of adding the two measured values taken substantially at the same position is almost lost. Besides, separate sampling before or after the measurement by using the oxygen concentration cell is a time-consuming and troublesome operation.

In an oxygen concentration measuring device using a solid electrolyte, it is necessary to provide two kinds of connections; namely, an electric connection between the solid electrolyte, and a mechanical connection for providing a standard gas to one side of the solid electrolyte. There has been a need for a simple mechanism capable of simultaneously accomplishing the aforesaid two connections, but no one has succeeded yet in providing such a mechanism.

SUMMARY OF THE INVENTION Therefore, the principal object of the present invention is to provide a device for acurately measuring the oxygen concentration of molten metal, which device is free from any of the aforesaid difficulties experienced in conventional devices for measuring oxygen concentration.

` An object of the present invention is to provide a device formeasuring oxygen concentration of molten metal by using a solid electrolyte, which device eliminates the risk of generating cracks in the solid electrolyte, so as to allow its dipping into a molten metal to be measured without preheating` the solid electrolyte together with its tubular` holder. g

'l Another o bject of the present invention is to provide a device for measuring oxygen concentration of molten metal by using a solid electrolyte, which device can prevent slag of the molten metal from entering between the Surface of the Solid electrolyte andthe molten metal when the device is dipped in the molten metal, so that solid electrolyte comes in contact Vwith clean moltenmetal free from slag.

Another object of the present invention is to provide a device for measuring the oxygen concentration of molten metal of the aforesaid type, which ensures gastight bondage of the solid electrolyte to its holder leven if it is dipped in the molten metal. y Y

It is an object of the present invention to provide a simple device for measuring oxygen concentration of molten metal, which can be kept in the molten metal for a time periody long enough for ensuring stable'measurement. The measuring device maybe equipped with a means for taking specimen of the molten metal for laboratory analysis.

Another object of the present invention is to provide a device for measuring oxygen concentration of molten metal, which simultaneously measures the oxygen concentration and collect a clean specimen of the molten metal for laboratory analysis, the composition of the specimen thus collected being substantially identical wiht that of the molten metal whose oxygen concentration is measured by the device at the time of the collection.

Another object of the present invention is to provide a device for measuring oxygen concentration of molten metal by using a solid electrolyte, in which electric connection from the solid electrolyte to an outside circuit is accomplished simultaneously with mechanical connection of the solid electrolyte to a standard gas supply passage.

BRIEF DESCRIPTION OF THE DRAWING The foregoing objects and other objects as well as the characteristic features of the invention will become more DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1x, a device for measuring oxygen concentration of molten metal comprises a solid electrolyte or a ceramic disk 1 gastightly secured to the lower end of a tubular holder 2 by a refractory adhesive 3. The holder 2 is carried by a protective tubing 4 and detachably connectible to a concentric dual metallic pipe means 5. The dual metallic pipe means 5 consists of an outer metallic tube 6 and an inner metallic tube 7, and it is electrically connected to a suitable indicator, e.g., a potentiometer 8, and mechanically connected to a standard gas source 9. The dual metallic pipe means 5 connected to the potentiometer 8 and the standard gas source 9 is repeatedly used, together with connecting means therebetween, but the device M illustrated in FIG. l consisting of the protective tubing 4, the tubular holder 2 carrying the ceramic disk 1 and so on are discarded after completing each measurement of the oxygen concentration of molten metal.

A standard gas chamber 10 is formed in the tubular holder 2 so as to cause the standard gas therein to come in contact with the ceramic disk 1 through a porous electrode 11 secured thereto. The porous electrode 11 is made of platinum, silver, nickel. or alloys thereof. For claritys sake, the electrode 11 is shown in all the figures as separated from the ceramic disk 1, but it is actually integrally secured to the ceramic disk 1. One end of a first lead wire 12 is connected to the porous electrode 11` hereinafter.

The connector 15 is generally of hollow cylindrical shape, and its upper edge fits in the space between the two metallic tubes 6, 7 of the concentric dual metallic pipe means 5, as shown in-FIG. 1. A central passage 16 is formed through the connector 15 along its central axis, and an inlet pipe 17 is tted in the passage 16 for communicating the standard gas chamber 10 of the tubular holder 2 with the inside of the inner tube 7. The connector also has a side passage 18, in which an outlet pipe 19 is inserted so as to communicate the standard gas chamberv 10 with the outside space of the concentric dual metallic pipe means 5.

The fixture means carries a reference electrode 20, which is disposed in the outside Vof the tubular holder 2 with a clearance therefrom. The lower end of a second lead wire` 21 is electrically connected to the reference electrode 20. The first and second lead wires 12 and 21 are gastightly buried in the refractory adhesive 14 and the connector 15 in such a manner that the upper ends of the lead wires 12 and 21 are connected to the inner and outer metallic tubes 7 and 6 of the concentric dual metallic tube means 5, respectively.

The protective tubing 4 consists of a hollow inner paper cylinder 22, a refractory mortar layer 23 applied on the outerperipheral surface of the paper cylinder 22 except its upper portion, and an outer paper shell 24 surrounding the outer surface of the mortar layer 23. The an-ge of the flanged sleeve 13 is secured to the mortar layer 23 of the protective tubing 4, as shown in FIG. l. As a result, the tubularholder 2 carrying the ceramic disk 1 protrudes-from the lower end of the protective tubing 4, and the tubular holder 2 is preferably surrounded by a heatresistant cap 25 secured to the bottom of the tubing 4.

The cap 25 is made of a suitable metal or porcelain, and it is provided with two or more holes 26, which are normally blocked by covers 27, respectively. The material ofthe cover 27 for blocking the holes 26 is such that it is carbonized when being dipped in the molten metal to be measured. ForU instance, the cover 27 is made of at least one of materials selected from the group consisting of paper, cloth, synthetic resin, and leather.

The purpose for blocking the holes 26 of the cap 25 is to prevent slag floating on the molten metal from entering into the inside of the cap 25. More particularly, when the device M for measuring the oxygen concentration is dipped into the molten metal, the cap 25 penetrates through the slag layer floating on the top surface of the molten metal until it reaches the molten metal to be measured. In the meantime, the covers 27 are carbonized by the heat of the'slag and the molten metal, but the carbonizing 'process of the covers takes a finite timewhich is long enough for preventing the slag from entering into the space between the tubular holder 2 and the heat-resistant cap 25. After the carbonized cover is separated from the cap together with slag sticking to the cover, the molten metal enters into the inside of the cap 25.

The cap 25 also acts to keep `the molten metal therein fairly stable or calm even Whenthe molten metal outside the cap is vigorously agitated. With such fairly stable or calm molten metal in the cap 25, fine particles of slag which are forced into the cap together lwith the molten metal may come upward and move out of the cap 25 through the holes 26. Thus, the molten metal in the proximity of the ceramic disk 1 can be kept free from the slag, so that the oxygen concentration of the molten metal per se can acmrately` be measured in a stable fashion. Such stabilizing effects of the cap 25 is partic` ularly advantageous for application to refining convertors.

In the preferred embodiment of the invention, as illustrated in FIG. l, the protective tubing 4 was about l meter long, and it was made by forming a 6.5 mm. thick inner paper cylinder 22 with a bias-wound paper layer, applying a 5 mm. thick refractory mortar layer 23 on the outer surface of the paper cylinder 22 with a kneaded mixture of magnesia, silica particles, clay, and water, and forming a 2 mm. thick outer paper shell 24 with another bias-wound paper layer on the outer surface of the mortar layer 23. It -was confirmed by tests that such protective tubing 4 can endure the heat of molten steel at l,650 C. for about 45 seconds without being burned down, due to its heat-resisting construction and the presence of adiabatic air layers between the mortar layer 23 and paper layers 22, 24. Accordingly, a suicient period of 30 to 35 seconds can be ensured for the measurement of the oxygen concentration of the molten steel by the device M according to the present invention, since 5 to 8 seconds is necessary from the immersion of the device in the molten metal to the beginning of the measurement.

The construction according to the present invention improves the durability of the device for measuring oxygen concentration of molten metal, as compared with that of conventional devices for similar purposes: namely, for instance, a conventional protective tubing consisting of a paper cylinder alone can endure the molten steel at 1,650 C. for only 13 seconds before the paper cylinder is burned down, so that time available for the measurement is at most 7 to 8 seconds; and another conventional protective tubing consisting of an inner paper cylinder and a refractory mortar layer can endure the molten steel at 1,650 C. for only about 30 seconds before the inner paper cylinder is burned down.

The inventors have further confirmed that the durability of the protective tubing in the molten steel at 1,650 C. up to 40 seconds, and the durability in molten steel in a ladle at l,550 C. up to 50 seconds, by forming the refractory mortar layer 23 with a mixture of alumina particles and aluminum phosphate applied on the bias-wound inner paper cylinder 22, and enhancing the heat-resistivity and the adiabatic effect of the outer paper shell 24 by impregnating water `glass therein. Furthermore, the inventors have succeeded in providing a durability of 50 to 55 seconds in molten steel at l,650 C. to 1,700 C., by forming the refractory mortar layer 23 with a mixture of silicon carbide, clay, and water, as applied on the bias-wound inner paper cylinder 22, and enhancing the heat-resisitivity of the outer paper shell 24 by impregnating ethyl silicate therein.

The material for the connector 15, as shown in FIG. 1, is preferably made of slightly flexible synthetic resin, such as polytetrafluoroethylene, polypropylene, and nylon. When the connector 15 is made of slightly flexible material, it can gastightly engage the lower end of the annular space between the inner pipe 7 and the outer pipe 6 of the concentric dual metallic pipe means 5. An insulating spacer 28 is inserted between the outer pipe 6 and the inner pipe 7, so as to electrically insulate the two pipes from each other, as shown in FIG. 1.

The arrangement of the ceramic disk 1 and its tubular holder 2 is not restricted to that as illustrated in FIG. l.

The 4heat-resistant cap 25 -may be dispensed with under certain conditions. More particularly, referring to FIG. 2, the ceramic disk 1 of the aforesaid embodiment may be replaced with a compressed cake of suitable solid electrolyte powders, which cake is directly carried by a tubular holder 2 without using any refractory adhesive. In the figure, an arcuately expanded portion 29 is formed at the lower end of the tubular holder 2, so as to provide a solid electrolyte chamber 30, wherein a compressed solid electrolyte cake 31 is fitted by stung a powder mixture to it under pressure, which powder mixture is a pulverized solid electrolyte, and the solid electrolyte, for

instance, consists of 85 mol percent of zirconium oxide and 15 mol percent of calcium oxide. A platinum wire 32 is connected to the compressed solid electrolyte cake 31 by inserting the lower end of the wire 32 in the powder mixture when the latter is stuffed to the chamber 30 under pressure. It is important here not to allow the lower edge of the wire 32 to protrude from the cake 31. In the embodiment of FIG. 2, the platinum wire 32 acts both as the porous electrode 11 and the rst lead wire 12 of the preceding embodiment, as shown in FIG. 1. Thus, a separate porous electrode 11 can be dispensed with.

Generally speaking, particles of porcelain materials are sintered when they are heated at a temperature above a certain level, and the sintering tends to reduce the volume of procelain materials. The aforesaid compressed cake 31 is made of those porcelain materials, so that it tends to shrink as it is heated in the molten metal to be measured. In order to compensate for such shrinkage of the compressed cake 31, the tubular holder 2 is made of special material, such as a heat-resistant glass mainly consisting of quartz, so that volume shrinkage of the solid electrolyte chamber 30 defined by such heat-resistant glass may be greater than the shrinkage of the compressed cake 31 when they are heated in the molten metal. Thus, the cake 31 is gastightly held by its tubular holder 2 in the molten metal. If the tubular holder is, however, made of other material which is less shrinkable than the cake 31, the gastightness of the joint between the cake 31 and its holder 2 is lost when they are dipped in the molten metal, because the shrinkage of the cake 31 may produce a gap between the cake 31 and the holder 2. Accordingly, the use of the aforesaid combination of the compressed cake and the tubular holder made of heat-resistant glass will ensure accurate measurement of the oxygen concentration without causing any leakage of the standard gas at the joint of the cake and its holder.

The heat-resistant cap 25 may be dispensed with by directly covering the lower end of the tubular holder 2 and the ceramic disk 1 with the same material as the aforesaid cover 27, as shown in FIG. 3. In the figure, the lower end of the reference electrode 20 is also enclosed by the cover material 27. When the tubular holder 2, as shown in FIG. 3, is dipped in molten metal to be measured, the molten metal reaches the ceramic disk 1 only after the cover material 27 is completely carbonized and separated from the cap. Thus, the ceramic disk 1 is preheated during the period when the cover material 27 is carbonized, so that the ceramic disk 1 is protected from thermal shock caused by immediate contact with the molten metal. Consequently, the risk of the cracking of the ceramic disk 1 by such thermal shock is completely eliminated. The cover material 27 also acts to carry away slag attached thereto, as the cover material 27 per se is carbonized and comes up to the surface of the molten metal. As a result, clean molten metal comes in contact with the ceramic disk 1 and the reference electrode 20, so as to ensure accurate measurement of the oxygen concentration of the molten metal.

The gastightness of the joint between the ceramic disk 1 and its tubular holder 2 can be improved by applying a suitable protector on the refractory adhesive therebetween. Referring to FIG. 4, a protector ring 33 is applied on the outer surface of the refractory adhesive 3 in such manner that the protector ring 33 bridges the peripheral edge of the ceramic disk 1 and the lower edge Aof the tubular holder 2 across the adhesive 3 on the side opposite to the standard gas chamber 10. In the case of measuring the oxygen concentration of molten steel, the protector ring 33 preferably consists of a paste made by kneading tile frit particles or similar glass particles 'while adding water therein, which particles have a softening temperature of 1,100 C. to 1,400 C. In the case of measuring the oxygen concentration of molten copper, the protector ring 33 may be made by using glass particles having a softening temperature of 700 C. to 900 C. A second protector ring 34 made of glass particles having a softening temperature of 400 C. to 700 C. may be disposed between the refractory adhesive 3 and the aforesaid protector ring 33, as shown in FIG. 5. In any case, the rstprotector ring 33 which comes in contact with the molten metal should be made of glass material having a softening temperature lower than the temperature of the molten metal by C. to 400 C.

With the protector ring or rings, as shown in FIGS. 4 and 5, the glass material of such ring or rings is softened when the device M is dipped in the molten metal to be measured, so as to lill up any gaps formed between the cearmic disk 1 and the lower edge of the tubular holder 2. Thus, the risk of the gas leakage between the standard gas chamber 10 and the molten metal is completely eliminated, for ensuring accurate and reliable measurement of the oxygen concentration. Without such protector ring or rings, the difference of heat expansion between the ceramic disk 1 and its tubular holder 2 may cause minute gaps therebetween, and the molten metal may short-circuit the current path from the reference electrode 20 to the porous electrode 11 through such minute gaps, so as to make the measurement meaningless. The protector ring or rings act to block such minute gaps and prevent the molten metal from short-circuiting the current pass. Thus, the protector ring or rings provide for dependable measurement of the oxygen concentration of molten metal.

In order to collect a specimen of the molten metal from the very spot where the measurement by the ceramic disk 1 is taken, a separate specimen chamber may be formed in the cap 25 of FIG. 1. Referring to FIG. 6, the heatresistant cap 25 includes an access space 35 defined below the ceramic disk 1 by a pair of partition walls 36 and 3-7 and a specimen chamber 38 below the access space 35. The side wall of the access space 35 has at least two holes 39, and the partition wall 37 between the access space 35 and the specimen chamber 38 has two or more small vertical holes 40 bored therethrough at its central portion. When the device M carrying such cap 25 is dipped in molten metal to be measured, the molten metal may enter into the cap 25 through the holes 26 so as to form an oxygen concentration cell across the ceramic disk 1 in the aforesaid manner. At the same time, the molten metal enters into the access space 35 through the side wall holes 39, and fills the specimen chamber 38 through the small vertical holes 40 of the partition wall 37. When the device M is removed from the molten metal upon completion of the oxygen concentration measurement, the device M is likely to be slanted, so that the molten metal in the access space 35 may be split out of the cap 25, but the molten metal in the specimen chamber 38 may be held there due to the bottle neck formed by the small lVertical holes 40 of the partition wall 37. Thus, the molten metal in the chamber 38 provides a specimen for laboratory analysis.

The construction of the specimen chamber 38 in FIG. 6 is particularly advantageous in providing pure specimen, because the small vertical holes 40 through the partition wall 37 act to prevent the slag from entering the specimen chamber 38. If an open dipper is used for collecting a specimen, the slag oating on the top surface of the molten metal inevitably enters into the dipper and contaminates the specimen of the molten metal.

In FIG. 6, the upper partition wall 36 of the access space 35 is provided for the following purposes. When the molten metal flows into the specimen chamber 38, the air is expelled from the chamber 38 through the small vertical holes 40, and the air may reach the ceramic disk 1 but for the partition wall 36. Thus, the partition wall 36 is to prevent such air from the specimen chamber 38 from reaching the' ceramic disk 1 and affecting the measurement of the oxygen concentration. If high accuracy is not required, the upper partition wall 36 may be dispensed with, as illustrated in the embodiment of FIG. 7'.

To illustrate the material and the. dimension of the heat-resistant cap 25, it may be pointed out that the cap 25 ofthe embodiment of FIGS. -1,f 6 and 71is made by sintering aluminum oxide, inclusive ofthe `partition walls, the access space, andfthe specimen chamber. Referring to FIGS. f6 `and7, the depth of the specimen chamber 38` was 1.3 cm., and the height of the access space 35 was 0.8 cm., and the diameter ofthe hole 39 was 0.5 cm., and thev diameter of the small hole 40 was 0.3 cm.

Referring to FIG. .8, a specimen chamber may be made separately and attached to the heat-resistant cap 25 of the preceding embodiment. In` the ligure, a separate -specimen chamber 41 is, for instance, made of. heatresistant stainless steel, in a manner similar to the access space 35 and the specimen chamber 38 of FIG. 6. Such separate chamber 41 can be attached to the heat-resistant vcap 25 only when a specimen of the molten metal is required for laboratory test. If the measurement of the -oxygen concentrationalone is sufficient, the separate spec- `imen chamber 41 is not attached to the heat-resistant cap 25, so that the economy of the measurement and the 'analysis is improved.

@Referring to FIG. 9, it is also possible to form a specimen chamber 38 by enlarging` the lower portion of a heat-resistant cap 25. In the figure, the specimen chamber 38 is formed so as to surround the lower portion of .the :heat-.resistant cap 25, and the inside of the .cap 25 is communicated with the. specimen chamber 38 through small holes 42 bored through the lower end of the side wall of the cap 25. Vent holes 43 are bored on the top wall of the specimen chamber 38 for allowing the air to escape therefrom. The specimen chamber 38 of FIG. 9 is made of mullite. v

` lIn order to measure the temperature of the molten ,metal whose oxygen concentration being measured, a thermoco'uplelnot shown) may be disposed in the proximity of the' reference electrode 20 at the outside of the tubular holder 2, with asuitable clearance from both of the electrode I20 and the holder `2. The thermocouple is preferably housed in an electrically insulating refractory protective pipe (not shown) made of alumina, mullite, quartz, etc. whichlprotective-pipe may be buried in the refractory adhesive 14 of the fixture means so as to extend along the tubularholder 2`substantially to the tip of the holder 2. Lead wires (not shown) of such thermocouple must be brought to the outside of the device M through the hollow protective tubing 4, while electrically insulating the leads from the concentric dual metallic tube means 5, so that the thermocouple may be connected to a suitable temperature indicator (not shown). When the cap 25 is used, the thermocouple should preferably be disposed inside the cap 25 but outside the tubular holder 2. With such a thermocouple disposed in the proximity of the reference electrode 20, the temperature of the molten metal is determined while measuring the oxygen concentration thereof, so that the accuracy of the oxygen concentration can further be improved with the knowledge of its temperature.

To protect the cap 25 and the tubular holder 2 during handling and transportation thereof, a suitable protective means (not shown), consisting of a metallic net (not shown) or the like, may be secured to the device M so as t enclose the holder 2 and the cap 25.

As described in the foregoing disclosure, according to the present invention, a substantially slag-free specimen of the molten metal can be collected from the same spot where the measurement of the oxygen concentration is taken, so that accurate correction of the voltage-oxygen concentation curves may be effected for ensuring reliable measurement of the free oxygen concentration. The accurate determination of the free oxygen concentration provides basis for meaningful comparison of the yfree oxygen concentration against the total oxygen in the molten metal. The simultaneous determination of the oxygen concentration based on the principle of oxygen con- Vten metal. f Y

. With the device for measuring the oxygen concentration of molten metal, according to the present invention,

A.the tubular holder of a solid electrolyte can be dipped into the molten metal to be measured Without being preheated, while protecting the solid electrolyte from cracking due to the thermal shock and preventing slag from coming in contact with the solid electrolyte. Thus, the

gastght joint of the solid electrolyte to its tubular holder is ensured throughout the measurement. Above all, the

solid electrolyte can be held in the molten metal for a sufficiently long period of time for ensuring reliable measurement of the oxygen concentration.

Furthermore, the electrical connection of the electrodes of an oxygen concentration cell to an indicator, such as a potentiometer, can easily be accomplished, simultaneously with the mechanical connection of the cell to a standard gas source. A clean specimen of the molten metal can be collected from the same spot where the oxygen concentration is measured, so as to enable the chemical analysis of the very metal whose oxygen concentration is measured by the solid electrolyte.

While several examples have been herein disclosed, it is obvious that various changes can -be made without departing from the spirit and scope of the invention as set forth in the appended claims. Further, it is to be understood that all matter hereinbefore set forth is to be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A device for measuring oxygen concentration in molten metal comprising,

an elongated hollow protective tubing,

a pair of spaced concentric metal tubes mounted in and spaced from the inner walls of said protective tubing,

an annular connector element disposed in a gastight manner within the annular space between and at the lower end of said concentric metal tubes,

tubular holder disposed at the lower end of said protective tubing and in communication with the opening in the lower end of said connector element, and extending below the end of said protective tubing,

a solid electrolyte secured in a gastight manner in the lower end of said tubular holder,

a refractory adhesive for securing said solid electrolyte within said tubular holder, and a layer of glass particles disposed on the outer exposed surface of said refractory adhesive, said glass particles having a softening temperature between about 1,1010 and 1,400 C.,

a porous electrode connected to the inner surface of said solid electrolyte and extending into said tubular holder,

a reference electrode extending downwardly from the bottom of said connector element on the outside of said tubular holder and spaced therefrom,

a lead wire connected to each of said porous electrode and said reference electrode and passing upwardly through said connector element and connected respectively to the inner and outer metal tubes of said pair of spaced concentric metal tubes, said connector element being provided with a passage communicating with the upper end of said tubular holder and the space between said protective tubing and said pair of concentric metal tubes, and

means for covering the lower end of said tubular holder and said solid electrolyte, said means including at least one carbonizable material selected from the group consisting of paper, cloth, synthetic resin and leather whereby said carbonizable material is carbonized when the device is introduced into molten metal and rises to the surface of the molten metal with any slag adhering thereto to permit access of clean molten metal to said tubular holder and the outer surface of said solid electrolyte thus increasing 1 1 theiaccuracy' of measurement of tion in said molten metal. t 2. A measuring device as claimed in claim.1'and further comprising a layer of glass particles having a softenoxygen concentraing temperature between about l400" and 700'Cg'` dis- ,1,5

posed between said first mentioned layer of glass particles and said solid'electrolyte.` y

3. A measuring device as claimed` in claim 1 wherei said covering means consists of carbonizable paper.r

4. A measuringdevice as claimed in claim 1 and further comprising a heatresistant cap secured to thelower end of said protective tubing to enclose the end of said tubular holder extending below the end of said tubing, said heat resistant cap being provided with at least two holes therethrough for admitting molten metal into said cap for contact with said tubular holder and said solid electrolyte, said covering means covering said at least two holes.

5. A measuring device as claimed in claim 4 wherein said heat resistant cap includes a specimen chamber for receiving a specimen of the molten metal when said carbonizable material is carbonized.

6. A device for measuring oxygen concentration in molten metal comprising,

an elongated hollow protective tubing,

a pair of spaced concentric metal tubes mounted in and spaced from the inner walls of said protective tubing,

an annular connector element disposed in a gastight manner within the annular space between and at the lower end of said concentric metal tubes,

a tubular holder disposed at the lower end of said protective tubing and in communication with the opening in the lower end of said connector element, and extending below the end of said protective tubing,

a solid electrolyte secured in a gastight manner in the lower end of said tubular holder, said solid electrolyte being a powder compressed into the form of a cake and the lower end of said tubular holder being provided with an arcuately expanded end portion for receiving and holding said compressed cake of solid electrolyte,

a porous electrode connected to the inner surface of 12 said vsolid electrolyte and extending' into said tubular holder, f i a reference electrode extending downwardly' from the bottom of said connector elementen the outside o said tubular holder and spaced therefrom, a lead wire connected to each of saidporous electrode and saidvreference electrode and passing upwardly through said connector element andconnected respectively to the inner and outer metal tubes of said -par of spaced concentric metal tubes, said connector element being provided with a passage communicating with the upper end of said tubularholder arid the space between said protectivetubing and Said pair of concentric metal tubes, and means for covering the lower end of said tubular holder and said solid electrolyte, said means including lat least one carbonizable material selected from the group consisting of paper, cloth, synthetic resin and leather whereby said carbonizable material is carbonized when the device is'introduced into molten metal and rises to the surface of the molten' metal with any slag adhering thereto to permit'access of clean molten metal to said tubular holder and the outer surface of said solid electrolyte thus increasing the accuracy of measurement of oxygen concentration in said molten metal. 7. A measuring device as claimed in claim 6 wherein said tubular holder consists of quartz glass. u

References Cited UNITED STATES PATENTS 3,442,773 5/1969 Wilson y204-195 S 3,468,780 9/1969 Fischer 204-195 S 3,616,407 10/1971 Engell et al. 204-195 S 3,619,381 11/1971 Fitterer 204-1 T 3,657,094 4/1972 Hans et al. 204-1'95 S FOREIGN PATENTS 1,537,804 7/1968 Francepn.' 204-195 S 1,191,222 5/1970 Great Britain 204-195 S TA-HSUNG TUNG, Primary Examiner v U.S. Cl. 'X.R. 204-1 T 

